1. Field of the Invention
The present invention relates to a semiconductor device having wiring layers with a reflection preventing film and a method of manufacturing the same. More particularly, the present invention relates to a semiconductor device having a configuration in which wiring layers having a reflection preventing film at least at the uppermost layer are covered with a protection film and a method of manufacturing the same. Still more particularly, the present invention relates to a semiconductor device which has a configuration in which wiring layers each having a reflection preventing film are connected to a nonvolatile memory element and the wiring layers are covered with a protection film and a method of manufacturing the same.
2. Description of the Related Art
As the semiconductor memory device into which stored information can be written freely on the user side, there are known nonvolatile memory devices such as an erasable and programmable read-only memory (EPROM), an electrically erasable and programmable read-only memory (EEPROM), etc.
As shown in FIG. 16, a nonvolatile memory element M in a nonvolatile memory device is mainly composed of a semiconductor substrate 1 formed of a p-type single crystal silicon substrate. The nonvolatile memory element M is formed in a region surrounded by a device separating insulating film (field isolation film) 2 on a principal plane of the semiconductor substrate 1.
The nonvolatile memory element M comprises a channel forming region, a first gate insulating film 3, a floating gate electrode 4, a second gate insulating film 5, a control gate electrode 6, and a pair of n-type semiconductor regions 8 employed as a source region and a drain region. The channel forming region is formed on a surface of the semiconductor substrate 1. In order to improve a information retaining characteristic, at least the floating gate electrode 4 is covered with a silicon oxide film 7 of fine film quality.
The nonvolatile memory element M is positioned at an intersection portion of a word line 6WL and a data line 11DL and is electrically connected to the word line 6WL and the data line 11DL. The word line 6WL is formed integrally with the control gate electrode 6 of the nonvolatile memory element M. Thus, the word line 6WL is formed of the same conductive layer as the control gate electrode 6. The data line 11DL is formed on an interlayer insulating film 9 which covers the nonvolatile memory element M. The data line 11DL is connected to an n-type semiconductor region 8, which is employed as the drain region, via a connection hole (a contact hole) 10 which is formed in the interlayer insulating film 9.
A protection film (passivation film) 12 is formed on the data line 11DL to cover the data line 11DL and the nonvolatile memory element M. In the nonvolatile memory device, a plasma CVD silicon oxide film which is formed by the plasma CVD method to enable fine film quality and low temperature film formation is employed as the protection film 12. The protection film 12 can enhance a retaining characteristic of information stored in the nonvolatile memory element M.
A method of manufacturing the above nonvolatile memory device will be explained with reference to FIGS. 17 to 19. First, as shown in FIG. 17, the nonvolatile memory element M is formed on the principal plane of the semiconductor substrate 1. The interlayer insulating film 9 to cover the nonvolatile memory element M is then formed. As shown in FIG. 18, the connection hole 10 is then formed in the interlayer insulating film 9 on the n-type semiconductor region 8 which is employed as the drain region of the nonvolatile memory element M.
Then, as shown in FIG. 19, the data line 11DL which is connected electrically to the n-type semiconductor region 8 via the connection hole 10 is formed on the interlayer insulating film 9. The data line 11DL is formed as an at least double-layered structure which consists of an aluminum alloy film 11A and a titanium nitride (TiN) film 11B being deposited on a surface of the aluminum alloy film 11A. The aluminum alloy film 11A is deposited by the sputtering method to have a film thickness of 800 nm. The TiN film 11B is employed as a reflection preventing film which can prevent excessive exposure caused by a halation phenomenon, which is generated by the reflection of light on a surface of the aluminum alloy film 11A, when an etching mask employed to pattern the data line 11DL is formed by the photo-lithography. The TiN film 11B is similarly deposited by the sputtering method to have a film thickness of 30 nm. The aluminum alloy film 11A and the TiN film 11B, after deposited, are patterned by the etching using the reactive ion etching (RIE) method.
Then, as shown in FIG. 16, the protection film 12 covering the data line 11DL is formed. As the protection film 12, the plasma CVD silicon oxide film which is formed by reacting an SiH.sub.4 gas, an N.sub.2 O gas, and an N.sub.2 gas in their plasma state at the substrate temperature of 400.degree. C. is employed.
Then, in order to reduce wiring resistance by increasing aluminum crystal grains of the aluminum alloy film 11A of the data line 11DL, sintering is performed. This sintering is performed in the forming gas atmosphere at the heat treatment temperature of 400.degree. C. to 450.degree. C. for about five minutes. A mixed gas of H.sub.2 and N.sub.2 (a flow rate ratio is H.sub.2 :N.sub.2 =1:9) is employed as the forming gas.
When a series of above manufacturing steps have been completed, the nonvolatile memory device is implemented.
In the above-mentioned nonvolatile memory device, following problems are not taken in consideration. With the larger capacity and higher operation speed in information reading of the nonvolatile memory device, a pattern of the data line 11DL is miniaturized more and more. The TiN film 11B serving as the reflection preventing film, which is formed on a surface layer of the data line 11DL, is essential for such miniaturization. If a nitrogen composition ratio of the TiN film 11B is increased higher, reflectance of the surface of the TiN film 11B is decreased, so that performance as the reflection preventing film can be enhanced. Therefore, such a process is carried out normally that, when the TiN film 11B is sputtered, a large amount of N.sub.2 gas is supplied to increase the nitrogen composition ratio of the TiN film 11B.
However, in case a reflection preventing function is enhanced by increasing the nitrogen composition ratio of the TiN film 11B, the N.sub.2 gas is escaped or evaporated from the TiN film 11B by the sintering process which is performed after the protection film 12 has been formed. For this reason, there has been the problem such that there is a high possibility that peeling of the protection film 12 and disconnection of the data line 11DL are caused due to generation of the N.sub.2 gas.
An enlarged sectional shape of a defective portion in the related art is shown in FIG. 20. As shown in FIG. 20, the N.sub.2 gas generated from the TiN film 11B pushes up the protection film 12 and creates a cavity 13 on the boundary between the data line 11DL and the protection film 12. As a result, the protection film 12 peels off the data line 11DL. In addition, due to the strong pressure of the N.sub.2 gas generated from the TiN film 11B, the data line 11DL is scraped out and then disconnected. An Ar gas as well as the N.sub.2 gas is contained in the gas generated from the TiN film 11B. Ar which is employed to generate the plasma atmosphere in sputtering is taken into the TiN film 11B. Such Ar being taken into is then discharged as the Ar gas.
In particular, in the nonvolatile memory device, since the plasma CVD silicon oxide film which has fine film quality is employed as the protection film 12 for the purpose of improving the information retaining characteristic, discharge routes for both inert gases of the N.sub.2 gas and the Ar gas are lost. Hence, the above peeling of the protection film 12 and the disconnection of the data line 11DL appear remarkably in the nonvolatile memory device. These facts have been found by the inventors of the present invention.
In addition, in order to prevent the peeling of the protection film 12 and the disconnection of the data line 11DL, the inventors of the present invention have tried to reduce the nitrogen composition ratio of the TiN film 11B by performing the heating process at about 400.degree. C. after the data line 11DL has been patterned. As a result, the peeling of the protection film 12 and the disconnection of the data line 11DL can be suppressed, nevertheless such a problem has newly arisen that aluminum hillock is generated in the aluminum alloy film 11A of the data line 11DL because of addition of the heat treatment step. An enlarged sectional shape of another defective portion as an issue in the related art is shown in FIG. 21. As shown in FIG. 21, the aluminum hillock 11a is grown from the patterned sidewall of the aluminum alloy film 11A in the lateral direction. In the event that the degree of growth is large, neighboring data lines 11DL are short-circuited by the aluminum hillock 11a.